Favorite fantasy RPG.
Well, D&D is certainly the one I've played the most, and it utterly dominates my shelf space. But it dominates my shelves by dint of many editions, multiple supplements, and the D20 Explosion. There are parts of the D&D experience I love (a good Forgotten Realms game, for instance). But in the grand scheme of things, it's not my favorite.
I'm very fond of 13th Age, but more in theory than practice. My one experience playing it was pretty terrible, to be honest, though that was on the GM as far as I'm concerned. Also, it's brilliantly designed to handle one particular type of D&D-ish play, a weird love-child of 4e and 3x. So, it's very difficult to hack it into something else. Maybe if I get some long-term play out of it, but for now, it's an interesting diversion.
The simple elegance of Barbarians of Lemuria is a thing of beauty. It doesn't try to be all games to all people. It's a sword and sorcery game whee magic is an untrustworthy, dangerous thing, and it does that wonderfully. Also, the simple measure of renaming Hit Points "Lifeblood" is genius. That said, I've never played more than a one-shot of it. It's a great game, but I need to play more before it's going to reach favorite status.
I am of the opinion that Greg Stafford's King Arthur Pendragon is among the greatest RPGs of all time. The system is simple but not unsophisticated, and it's treatment of Passions, Loyalty, and Religion was ground-breaking. The notion that all PCs are of the same class is likewise, brilliant. It's also a very tough sell amongst the folks I've had in my gaming groups. That lack of actual play experience keeps it from the top spot.
So, that leaves me with a tie. Seriously, I can't choose. My first exposure to RuneQuest was like hearing Eddie Van Halen's "Eruption" for the first time. Everything irrevocably changed. I dove in to RQ and played nothing else for months, making my way through the minutia of Glorantha lore. I immersed myself in Battle Magic, Strike Ranks, and sectional armor. It was a deep and abiding love.
Then, Stormbringer came along. In high school, I read the DAW Elric novels more times than Tolkien. I remember walking into the game store at Central Park Mall (yes, by that point, there was a game store in the mall, called "Expensive Toys For Big Boys," and later "Intellectrics") and seeing that Frank Brunner cover on the original boxed set. It was everything I'd hoped for: a faster, leaner version of the rules I was used to, the potential for crazy disparate power levels, and a game that felt like the gonzo craziness of Moorcock's greatest creation. I got so much use out of it. So many terrific games. But I probably wouldn't have gotten it in the first place if RQ hadn't shown me a different approach to fantasy games.
So, there you go.